<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
      margin: 0;
      padding: 0;
    }
    html, body {
      height: 100%;
    }
    .left {
      float: left;
      height: 100%;
      width: 200px;
      background-color: yellowgreen;
    }
    .right {
      float: right;
      height: 100%;
      width: 200px;
      background-color: blueviolet;
    }
    .middle {
      margin-left: 200px;
      margin-right: 200px;
      height: 100%;
      background-color: pink;
    }
  </style>
</head>
<body>
  <!-- float + margin -->
  <div class="left"></div>
  <div class="right"></div>
  <div class="middle"></div>
</body>
</html>